The present invention relates to a pattern formation method, and more particularly, it relates to a pattern formation method of forming a resist pattern used for forming a semiconductor device or a semiconductor integrated circuit on a semiconductor substrate by using exposing light of a wavelength of a 1 nm through 180 nm band.
As exposing light used in forming a resist pattern through pattern exposure of a resist film formed on a semiconductor substrate, KrF excimer laser has been put to practical use. Also, a device including a semiconductor device or a semiconductor integrated circuit formed by using a resist pattern obtained by the pattern exposure using the KrF excimer laser is almost commercially available.
In this case, a resist material including a phenol resin is mainly used as a resist material to be pattern-exposed with the KrF excimer laser.
For further refinement of a semiconductor device or a semiconductor integrated circuit, ArF excimer laser with a shorter wavelength than the KrF excimer laser is used as the exposing light. A resist material including an acrylic acid type resin is mainly under examination as a resist material used in the pattern exposure with the ArF excimer laser.
In order to realize further refinement of a semiconductor device or a semiconductor integrated circuit, however, it is necessary to use, as the exposing light, a laser beam with a wavelength shorter than that of the ArF excimer laser, such as a Xe2 laser beam (with a wavelength of a 172 nm band), a F2 laser beam (with a wavelength of a 157 nm band), a Kr2 laser beam (with a wavelength of a 146 nm band), an ArKr laser beam (with a wavelength of a 134 nm band), an Ar2 laser beam (with a wavelength of a 126 nm band) or a soft X-ray beam (with a wavelength of a 13, 11 or 5 nm band).
Therefore, the present inventors have formed a resist pattern from a resist film of a known resist material through pattern exposure using a F2 laser beam. Now, a method of forming a resist pattern from a known resist material will be described with reference to FIGS. 6(a) through 6(d).
First, a resist material having the following composition is prepared:
Then, as is shown in FIG. 6(a), the resist material having the aforementioned composition is applied by spin coating on a semiconductor substrate 1, thereby forming a resist film 2 with a thickness of 0.5 xcexcm.
Next, as is shown in FIG. 6(b), the resist film 2 is irradiated with a F2 laser beam 4 through a mask 3 for pattern exposure. In this manner, an acid is generated from the acid generator in an exposed portion 2a of the resist film 2 while no acid is generated in an unexposed portion 2b of the resist film 2.
Then, as is shown in FIG. 6(c), the semiconductor substrate 1 is heated with a hot plate, for example, at 100xc2x0 C. for 60 seconds.
Thereafter, the resist film 2 is developed with an alkaline developer, such as a 2.38 wt % tetramethylammonium hydroxide developer. Thus, the resist pattern is formed.
The resultant resist pattern 5 has, however, a defective pattern shape as is shown in FIG. 6(d).
The resist pattern 5 similarly has a defective pattern shape not only when the F2 laser beam is used as the exposing light but also when light of a wavelength of a 1 nm through 180 nm band is used.
In consideration of the aforementioned conventional problem, an object of the invention is forming a resist pattern in a good pattern shape through pattern exposure using light of a wavelength of a 1 nm through 180 nm band as exposing light.
The present inventors have concluded that the resist pattern has a defective pattern shape because the resist film has a high absorbing property against light of a wavelength of a 1 nm through 180 nm band, and examined various means for decreasing the absorbing property against light of a wavelength of a 1 nm through 180 nm band. As a result, it has been found that the absorbing property of the resist film against light of a wavelength of a 1 nm through 180 nm band can be decreased when the resist material includes a halogen atom, a cyano group, a nitro group, an alkoxy group, an amino group, an alkyl group, a trifluoromethyl group or a mercapto group.
Then, the inventors have examined the reason why the absorbing property against light of a wavelength of a 1 nm through 180 nm band can be decreased when the resist material includes a halogen atom, a cyano group, a nitro group, an alkoxy group, an amino group, an alkyl group, a trifluoromethyl group or a mercapto group. As a result, it has been found that such an atom or a group has a property to shift the absorption wavelength band against the exposing light inherent in the resist material or to decrease the absorbing property of the resist material against light of a short wavelength band.
Now, referring to FIG. 1, an example to verify that the peak of a light absorption wavelength of a resist material against exposing light is shifted toward a longer wavelength when a base polymer of the resist material includes an amino group will be described.
FIG. 1 is a graph for explaining that the absorption zone of the exposing light is shifted by substituting an amino group for an aromatic ring of poly(vinyl phenol). In the graph of FIG. 1, a broken line indicates the absorption wavelength of poly(vinyl phenol) in which an amino group is not substituted for the aromatic ring; and a solid line indicates the absorption wavelength of an o,o-2 substitution product obtained by substituting an amino group for the aromatic ring of poly(vinyl phenol). As is understood from FIG. 1, the peak of the absorption wavelength, which is a 190 nm band when an amino group is not substituted, is shifted toward a longer wavelength by approximately 30 nm when an amino group is substituted.
When the peak of the absorption wavelength zone of the resist film is a 190 nm band, the resist film has poor transmittance against a F2 laser beam with a wavelength of a 157 nm band. However, when the peak of the absorption wavelength zone is shifted from a 190 nm band toward a longer wavelength by approximately 30 nm, the transmittance against the F2 laser beam is increased.
Also Japanese Laid-Open Patent Publication No. 60-254041 discloses a resist material including fluorine, that is, one of halogen atoms, in its base polymer. This resist material includes, in the polymer, xcex1-trifluoromethyl acrylic acid and an ester of alcohol having an electron attractive group as one repeating unit. The publication describes that the sensitivity of the resist material against an electron beam can be thus improved.
However, while an electron beam is used as exposing light in the description of Japanese Laid-Open Patent Publication No. 60-254041, the exposing light is light of a wavelength of a 1 nm through 180 nm band in this invention, and thus, the exposing light is completely different in the wavelength band. Furthermore, while the base polymer includes a halogen atom for the purpose of improving the sensitivity against an electron beam in the description of Japanese Laid-Open Patent Publication No. 60-254041, the polymer includes a halogen atom for the purpose of improving the transmittance against exposing light of a wavelength of a 1 nm through 180 nm band in this invention. Thus, these techniques are completely different in the technical idea.
Specifically, the pattern formation method of this invention comprises a resist film forming step of forming a resist film by applying, on a substrate, a resist material including at least one atom or group selected from the group consisting of a halogen atom, a cyano group, a nitro group, an alkoxy group, an amino group, an alkyl group, a trifluoromethyl group and a mercapto group; and a pattern forming step of forming a resist pattern by irradiating the resist film with exposing light of a wavelength of a 1 nm through 180 nm band for pattern exposure and developing the resist film after the pattern exposure.
In the pattern formation method of this invention, since the resist material includes a halogen atom, a cyano group, a nitro group, an alkoxy group, an amino group, an alkyl group, a trifluoromethyl group or a mercapto group, the absorption wavelength of the resist film against the exposing light is shifted toward a longer wavelength, or the absorbing property of the resist film against the exposing light of a short wavelength is decreased. Accordingly, the absorbing property against light of a wavelength of a 1 nm through 180 nm band can be decreased, and hence, the transmittance against light of a wavelength of a 1 nm through 180 nm band can be increased. As a result, a resist pattern can be formed in a good pattern shape through the pattern exposure using light of a 1 nm through 180 nm band as the exposing light.
In the pattern formation method, the atom or group is preferably bonded to a main chain, a side chain, a hetero ring or carbon constituting a double bond of a base polymer of the resist material.
In the pattern formation method, the atom or group is preferably a halogen atom bonded to an ester portion of an acrylic resin serving as a base polymer of the resist material.
In the pattern formation method, the resist material is preferably a chemically amplified resist.
When the resist material is a chemically amplified resist, the atom or group is preferably included in a protecting group of a base polymer, a crosslinking agent or an agent for inhibiting dissolution of the base polymer of the chemically amplified resist.
In the pattern formation method, a base polymer of the resist material preferably includes poly(vinyl phenol), poly(vinyl alcohol), an acrylic acid, a novolak resin or a derivative thereof in which a fluorine atom is substituted for a hydrogen atom.
The pattern formation method of this invention preferably further comprises, between the resist film forming step and the pattern forming step, a step of forming, on the resist film, a water-soluble polymer film from a water-soluble polymer including a halogen atom, a cyano group, a nitro group, an alkoxy group, an amino group, an alkyl group, a trifluoromethyl group or a mercapto group.
In this case, the water-soluble polymer is preferably polyacrylic acid, poly(vinyl alcohol), poly(vinyl pyrrolidone) or polystyrenesulfonic acid.
Alternatively, the pattern formation method of this invention preferably further comprises, between the resist film forming step and the pattern forming step, a step of forming, on the resist film, a water-soluble polymer film from a compound including a halogen atom, a cyano group, a nitro group, an alkoxy group, an amino group, an alkyl group, a trifluoromethyl group or a mercapto group, and a water-soluble polymer.
In this case, the compound is preferably trifluoroacetic acid, trifluoromethylsulfonic acid-or a surfactant including fluorine.
Also in this case, the water-soluble polymer is preferably polyacrylic acid, poly(vinyl alcohol), poly(vinyl pyrrolidone) or polystyrenesulfonic acid.
In the pattern formation method, the exposing light is preferably a F2 laser beam or an Ar2 laser beam.